A large number of water desalination and ion separation processes, such as reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD), depend on membranes for ion and organic matter removal. Although conventional membranes currently used in the separation industry are typically reliable and exhibit good separation performance, such materials often degrade when exposed to high temperatures and corrosive media (such as Cl2, acids, bases and certain organic compounds). Further, fouling associated with particulate deposition, scaling and biofouling decrease the membranes' permeation rates and ultimately contribute to costly system maintenance. Degradation problems are especially prevalent in the Arabian Gulf, due to high salinity, high turbidity and elevated temperatures of the water. In order to operate in such environments, ultrafast water permeation membranes with good mechanical properties are critical for water purification and desalination.
A membrane should, ideally, be ultrathin (for high flux permeation), mechanically strong to withstand applied pressures, and have tunable pore distributions for excellent selectivity. Recently, nanostructures such as zeolites, metal organic frameworks, ceramics and carbon-based materials have attracted considerable attention as alternative membrane materials, specifically due to their relatively good chemical resistance, high flux, and high rejection rates. However, zeolite membranes have failed to realize economical fabrication on a large scale due to manufacturing costs, reproducibility and defect formation. Further, ceramic membranes are very brittle under high pressures, which limits their practical applications in membrane technologies.
Although it is possible to fabricate high-flux and high selectivity membranes from carbon nanotubes (CNTs), it is currently difficult to synthesize highly aligned and high density CNTs with large lengths. CNTs remain an active area of research for membrane technologies, but costs and operational issues have greatly hindered the development and integration of CNTs into large area membranes. Graphene oxide (GO) nano-sheets (i.e., sheets of two-dimensional material) have emerged recently as a new class of ultrathin, high-flux and energy-efficient sieving membranes. However, despite the great potential of nano-porous GO membranes, scalable production has been hindered by difficulties in fabricating large-area uniform GO membranes by spin coating and vacuum filtration techniques. Further, experimental studies have failed thus far to confirm theoretical predictions of orders of magnitude improvement in the membranes' selectivity and permeability when compared to current state-of-the-art filtration. Transport measurements through graphene have been limited to microscopic areas with few pores or multilayered graphene-oxide. Experimental findings in GO membranes showed that molecules travel a tortuous path through the interlayer region between flakes, and while such membranes have demonstrated selective transport, the measured permeability does not match the expected performance of porous single-layer graphene due to this longer path length.
Thus, a two-dimensional metal carbide desalination membrane addressing the aforementioned problems is desired.